The present invention relates to a threading tap for cutting threads in primarily titanium and titanium-based metal alloys, comprising an elongate shaft of a metallic compound material, which at one end is provided with two or more lands preferably extending helically around the central axis of the tap, which lands on their envelope surfaces are provided with cutting threads of similar profile and which are separated by equally helically twisted chip flutes.
Threads are produced by chip-cutting or plastic forming methods. Threading by threading taps belongs to the chip-cutting methods. One may use either ready taps or series taps, depending upon the hardness and cutting data of the workpiece. Using ready taps, the thread is made by one single tap while using series taps, several taps are used in sequence for obtaining a ready thread.
Threading taps are normally made of high speed steel (HSS). In order to improve their function, HSS threading taps have sometimes been subjected to some sort of surface treatment. The most common surface treatments are steam tempering, nitration and coating with TiN. These treatments contribute to the counteracting of built-up edges, the increasing of surface hardness and wear strength and to lowering the friction. In spite of this, it has often turned out to be difficult to attain satisfactory threading in some difficult to machine materials. In particular, in tough materials such as titanium and titanium-based alloys, the usual threading taps of HSS have demonstrated unsatisfactory tool lives. Also, the quality of the thread has often been inadequate, which is caused by portions of the relatively tough material being stuck upon the threading tap, in particular at low cutting speeds. Such inconveniences are, of course, particularly aggravating in technical fields with highly strict safety requirements as in the aircraft industry.